Laminitis Overview and Anatomy

The equine hoof is a complex anatomical feature that plays a critical role in horse health.

Photo: Erica Larson, News Editor

Laminitis, also referred to as "founder," is an often devastating disease of the hoof that can cripple or kill afflicted horses. It's such an important equine disease that each year veterinarians, farriers, and horse owners from throughout the United States gather at the International Equine Conference of Laminitis and the Equine Foot.

At the 2012 conference, held Nov. 2-3 in Monterey, Calif., Nora Grenager, VMD, Dipl. ACVIM, of Grenager Equine Consulting in Middleburg, Va., presented an overview of laminitis and the anatomical structures of the hoof and lower leg that it affects.

The equine hoof is a complex anatomical feature that plays a critical role in horse health. "Hooves carry all the weight of the horse, yet are relatively small," Grenager said. "That means hooves need to be flexible, strong, and resilient."

And, in the healthy horse, a hoof is all of those things--the perfect structure to support and propel an athletic quadruped prey animal. However, when things go wrong in the hoof, they tend to go very wrong due to the complexity of the structure within the restrictive hoof capsule, Grenager said. Laminitis is one of those very big problems. It's so big, in fact, laminitis is a leading cause of death in horses, second only to colic. And while not always fatal, 15% of all horses will suffer a bout of laminitis in their lifetimes.

To understand what laminitis is and how it affects the horse, it's important to have at least a rudimentary understanding of the structures in play during a laminitic episode. With that in mind, Grenager outlined the hoof anatomy involved for the horse owners in attendance at the 2012 Laminitis Conference.

Those structures include the:

Hoof wall--The hard, exterior "capsule" of the hoof.

Coffin bone (also called the third phalanx, P3, or pedal bone)--The largest, hoof-shaped bone within the hoof capsule.

Laminae--Velcrolike tissues within the hoof that suspend the coffin bone inside the hoof wall.

Deep digital flexor tendon (DDFT)--A tendon that attaches to the back of the coffin bone and runs up the backside of the hoof. "The DDFT is a large component of how a horse flexes his foot each time he takes a step," Grenager explained.

Frog--The v-shaped, calluslike cushion on the underside of the hoof.

Sole--The bottom of the hoof.

So, how do these structures work together and, in the case of laminitis, fail together?

In the simplest terms, laminitis is the inflammation of the laminae within the horse's hoof. Each hoof includes 550 to 600 primary lamellae, each with 150 to 200 secondary lamellae. These tissues offer shock absorption during locomotion, holding the coffin bone in place and supporting the horse's entire bodyweight against gravity during movement.

When inflammation of the laminae occurs, the tissues within the hoof capsule fail, and the coffin bone is no longer fully supported within the hoof. With continued weight-bearing and movement of the horse, this can cause the coffin bone to rotate within the hoof or to sink toward the ground. The latter, commonly referred to as a "sinker," happens when the laminae throughout the hoof break down; the former occurs when laminae near the toe fail. Both can result in protrusion of the coffin bone through the sole of the hoof.

Regardless of whether the coffin bone comes through the sole, the result of laminitis is a painful, debilitating, and potentially deadly failure of basic hoof function.

About the Author

Michelle Anderson serves as The Horse's digital managing editor. In her role, she produces content for our web site and hosts our live events, including Ask the Vet Live. A lifelong horse owner, Anderson competes in dressage and enjoys trail riding. She's a Washington State University graduate (Go Cougs!) and holds a bachelor's degree in communications with a minor in business administration and extensive coursework in animal sciences. She has worked in equine publishing since 1998. She currently lives with her husband on a small horse property in Central Oregon.

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